1. Field of the Invention.
The present invention relates to extension ladders and more particularly to a vehicle supported extension ladder adapted for lying in a retracted horizontal position during travel of the vehicle and to be raised at an angle for use.
2. Description of the Prior Art.
Portable telescoping derricks or aerial ladders are well known and have usually included elongated hydraulic cylinders and piston rods to achieve the extending and retracting action of the several sections, such as shown by U.S. Pat. No. 2,923,381. Other load lifting devices, generally known as booms, feature a plurality of sections telescoping into each other and each being actuated by a separate hydraulic cylinder, such as shown by U.S. Pat. No. 3,721,054.
The principal objection to the use of elongated cylinders and piston rods is maintaining sufficient rigidity of the telescopically extended sections to prevent lateral movement of the extended piston rod and damage thereto and leaking of hydraulic fluid. Another objection to aerial ladders, as shown by the prior art, which employes a plurality of hydraulic cylinders for extending or retracting the ladder or boom has been the time delay in extending and retracting the plurality of sections wherein one cylinder must be extended or retracted before the next hydraulic cylinder is actuated for the respective direction of movement.
This invention provides a sturdily constructed plurality of relatively lightweight telescopically extensible and retractable ladder sections which are actuated for the telescoping movement by a single double acting-double end hydraulic extension cylinder mounted in the base ladder section and connected by cables and pulleys with the remaining ladder sections in a manner to obtain longitudinal extension and retraction of the movable ladder sections on a ratio movement for each ladder section of six units of distance for each unit of extension or retraction of the hydraulic cylinder piston rod.